The experiments proposed here exploit a newly developed cell binding assay that has dissected the process of cellular adhesion into a series of defined events that can be studied separately. The molecular basis for initial recognition events can now be studied in isolation without complications arising from subsequent cellular processes. Already observed during the initial binding phase has been a Ca++-dependent and a Ca++-independent component, recognition specificyt, differential initial strengths, and an ability to relate binding site number with cell-cell dislodgment force. The components of initial binding and subsequent processes will be approached, first by isolating events through experimental manipulation of the binding assay, then by a focused attack on each individual event. To screen for cell-surface molecules that participate in initial binding, monoclonal antibody technology has been adopted and will be continued. Another aspect of the proposed research centers on ligatin, a plasma membrane protein that functions as a cell-surface baseplate for peripheral glycoproteins. The family of glycoproteins associated with ligatin will be studied biologically and biochemically to determine their roles at the cell-surface, especially their possible contribution to adhesive mechanisms. In addition, the recognition between ligatin and the glycoproteins it binds seems to be due to a specific oligosaccharide containing phosphate. The structure and synthesis of this carbohydrate will be pursued. Our final aim is to begin to apply the probes that will be developed to phenomena more directly related to morphogenesis in vivo.